by ericmark »
Fri Feb 01, 2008 7:18 pm
There are a whole host of RCD’s
First looking at milliamps they will trip at starting at 10ma used to feed garden items when sockets are already on a 30ma and discrimination is required both at 40ms.
Then the standard personal protection type 30ma at 40ms.
Then where the earth is not good enough the milli-amps is calculated and you are allowed 70ms.
Then for fire protection 300ma is used.
And the list goes on. Also passive and active are available the active are often used for machine tools.
Looking at the first two price is a big factor. This is all because of market demands and current sizes. One which only handles 13 amp tends to be cheaper than one able to handle 100 amps. But demand driven prices has resulted in it being cheaper to completely renew a consumer unit than fit 3 single sockets. So what seems the best idea technically may be silly once you compare prices.
If you have for example one socket which is used outside then I would fit a 10ma at 40ma socket then if latter a consumer unit is changed you will still have discrimination. And I would also use an active type then if you lose power it will not auto-start until you press button. In a consumer unit I would use a passive type.
The RCBO’s are expensive when you need a few but for example with a cooker outlet with 13Amp socket using an RCBO’s on the non RCD side does alleviate the cumulative effect. Some use a double space and you may need a bigger consumer unit to fit the number of outlets you require.
RCD’s can be affected by external influences especially anything producing a magnet field so should always be tested after fitment. This combined with the Part P regulations etc. means it would be better fitted by an electrician.
The rules and regulations are getting harder and harder to satisfy but as yet there is nothing to say you must upgrade to the latest edition but once you do it your not allowed to go back to old edition. RCD’s can have problems with nuisance tripping I always test the house first and advise the house holder if I find anything that may be need repairing at the same time in order to hold in the trip I advise them first but not all do this and I have seen where for example the cooker has been disconnected as it was faulty and would trip out the RCD. Yes it did need renewing and the electrician was not trying to get extra work but unexpected expense is rarely welcome better to know before the job starts.
